1. Field of the Invention
The present invention, in general, relates to saws used for the cutting of timber and, more particularly, to pruning saws for the cutting of branches.
Pruning saws are well-known. They are used to cut limbs and small branches off of trees, shrubs, and bushes; a process that is often generally referred to as “limbing”. The limbs (i.e., branches) that are to be cut are generally disposed at an elevated position above a person (i.e., operator) who is standing on the ground while cutting them.
This, in turn, requires the user to extend a cutting blade sufficiently far away from the operator to make contact with the limb. The pruning saw provides this reach and allows the operator to place the cutting blade on the limb where a cutting of it is desired.
Operators who prune trees commercially will use customized equipment that allows them to better access the limbs. They may use an extendible mobile platform, sometimes referred to as a “cherry picker” to reach the limbs. A chainsaw is then commonly used to cut the limbs.
Homeowners and more occasional users (i.e., those who have a need to prune a number of limbs but not to the extent that a commercial tree service user might have) do not have access to the extendible mobile platforms and many people feel especially uncomfortable when using a chainsaw.
Alternately, commercial pruning operators will climb into the trees that are to be pruned, often carrying a chainsaw with them. They typically wear a safety harness and use additional gear to help prevent a possible fall from occurring.
Homeowners and the more occasional user are not apt to feel comfortable climbing trees nor are they likely to have the requisite safety gear.
To satisfy the pruning needs of the homeowner or the more occasional user, a certain common type of pruning saw is used that includes a fixed-position saw blade that is attached at an end of a pole. The pole may or may not be extensible. If the pole is extensible, its overall length can be varied within a narrow range. Therefore, the saw blade can be disposed a variable distance from a user within the length of the pole.
After extending the blade a desired amount and placing the saw blade where desired on the limb, the user then manually reciprocates the entire pole back and forth while maintaining the saw blade in the desired position. The saw blade, being attached to the pole, also reciprocates. It generally only cuts during a cutting stroke portion of the cycle that draws the blade (and pole) back toward the user. It does not cut during the opposite (i.e., retraction) stroke unless the blade is of a special type that cuts in both directions.
A first disadvantage of this type of pruning saw is that a greater mass, specifically the entire combined mass of the pole and the saw blade, must be reciprocated in order to sever (i.e., saw through) the limb. This, therefore, substantially increases the amount of physical work that is required.
Consequently the user is apt to become quickly fatigued. Because of this, these types of pruning saws are generally used for highly intermittent, light-duty, pruning needs where only a few limbs are to be cut at any given time.
For the typical homeowner or occasional operator, having to use a fixed-blade type of pruning saw to sever more than a few limbs at any given time is too tiring to accomplish. However, many homeowners have a great many trees, shrubs, and bushes that require periodic limbing. In particular, overhead limbs on fruit trees or limbs on other types of shade or decorative trees may require tens or even hundreds of limbs to be pruned at a time, for example, annually.
Fixed-blade, pole-mounted pruning saws are impractical whenever a large number of limbs require pruning yet they have been the only close-to-practical option available for the homeowner or occasional user. This is primarily because of the low cost of fixed blade pruning saws. Another reason for their popularity is that they are easy to use and therefore very little skill or training is required in order to use them.
Another disadvantage of fixed-blade, pole mounted pruning saws is that it takes a long time to sever each limb. As mentioned earlier, the entire pole and blade together must be manually reciprocated. Because of the large mass involved, the repetition rate is low, typically only about one stroke per second, at best. This makes each cut especially slow to accomplish. This, combined with the fatigue factor mentioned above, make these types of pruning saws impractical for all but the smallest of jobs.
The only known way to extend the reach of such types of pruning saws is to add, for some models, an extension segment at the bottom of the pole that increases its overall length. However, while this increases the overall reach it has no effect on the extensible portion. It increases the total mass which makes cutting that much the slower to accomplish.
There is another general disadvantage of fixed-blade pole-mounted pruning saws and also of other types of pruning saws, including motor driven types, and that disadvantage relates to the angle of the blade with respect to a remaining portion of the saw. Typically, a longitudinal axis of the blade of the pruning saw is nearly parallel with a longitudinal axis of the pole (or main body) of the pruning saw.
It is also preferred to have the longitudinal axis of the blade nearly horizontal during cutting of the limb so that gravity supplies at lease some of the force that urges (i.e., maintains) the blade in contact with the limb during its cutting.
Accordingly, when attempting to limb a branch that is directly overhead, the user must stand underneath the limb or nearly so. This results in three substantial additional disadvantages.
First, the longitudinal axis of the linear blade (the blade may not be linear and can include a slightly concave cutting surface) tends to be disposed very nearly vertical during a cutting of the limb. As the operator (i.e., user) progresses with a cutting of the limb, the limb begins to sag downward under the pull of gravity. As it sags, it begins to pinch the lower portion of the saw blade. This increasingly makes it difficult for the user to force the pinched saw blade up and down to continue cutting.
A second difficulty encountered by a nearly vertical saw blade is that in order for the blade to actually cut the limb, the cutting teeth of the blade must be urged into contact with the limb and held in contact with the limb under pressure during cutting. When the saw blade is nearly vertical, the operator must supply virtually all of the force necessary to maintain the blade in contact with the limb throughout the cutting of the limb. This is also fatiguing.
When the limb, as mentioned above, begins to sag and pinch the saw blade it becomes increasingly difficult for the user to supply the force necessary to maintain the cutting edge of the saw blade, under pressure, in contact with the limb.
A third difficulty encountered by a nearly vertical pruning saw blade is that when the limb is finally severed, it falls downward toward the operator. Clearly, this is dangerous.
Even if the operator is able to stand slightly off to the side with respect to a directly vertical fall-line of the limb (i.e., in line with gravity), there is still considerable danger to the operator. This is because the limb itself typically has branches that extend outward from a main trunk of the limb that is being severed. As the severed limb falls, the limb can rotate thereby disposing some of its longer branches over the operator as the limb continues to fall.
Some of these longer branches may not have even been visible to the operator because they were disposed above the limb during its cutting. In an original overhead position, the weight of these branches that are attached to the limb can cause them to sag downward toward the main trunk. An initial upward glance, if they were spotted, would cause them to appear smaller than they are and to not pose a risk of striking the operator.
But as the severed limb falls and rotates, these branches cease to sag as gravity ceases to pull them closer toward the main trunk of the falling limb. Accordingly, they extend further away from the main trunk of the limb where they pose an ever increasing hazard of impacting the operator as the severed limb falls.
Additionally, as the limb falls it may increase its rate of rotation about a longitudinal axis of the main trunk. Whenever such rotation occurs, centrifugal force also occurs. The centrifugal force, then, further urges the limb branches away from the main trunk of the falling limb. This extends the distance the branches are disposed away from the main trunk of the limb which, in turn, further increases their risk of striking the operator.
Clearly, there are many disadvantages that arise when an operator is disposed too close under a limb that is being severed. Accordingly, there is a need for an operator to stand even further away from the line of gravity that extends downward from a limb that is being severed.
With all of these substantial disadvantages, one might wonder why they are so popular. These types of fixed-blade pruning saws are reasonably priced and they are also generally light in weight. Also, the disadvantages as mentioned herein, are not generally known until after they have been purchased and used.
Certain types of motor-driven pruning saws could help ameliorate some of these difficulties, yet they tend to be heavy and expensive. This is because the user must purchase both the saw blade, motor, and drive mechanism. Of these, the motor tends to be especially expensive. It is desirable to provide for a homeowner or occasional user a motorized pruning saw when a greater number of limbs are to be severed that was less expensive than currently available models. If such a saw could be adapted for use with an external type of motor common to most households, such as is found on an electric drill to supply the motive force, it would be beneficial. A lower cost motorized pruning saw would be provided.
Another disadvantage of known types of motorized pruning saws is that the drive mechanism to supply power to the blade is generally heavy. Also, prior art types of motorized pruning saws either do not allow for extensible range (i.e., reach) or they are heavy, expensive, difficult to use, dangerous to use, or otherwise impractical for the homeowner or occasional user.
Prior art types of motorized pruning saws also fail to orient the longitudinal axis of the blade at a near horizontal position. This position is ideal during cutting because it maintains downward force on the blade and also because it helps dispose the operator a safe distance away from the line of gravity. However, in order for this to occur the reach must be variable because the safe-operating distance that the user (operator) must stand off from the line of gravity increases with the height of the limb that is being severed.
Prior motorized types of pruning saws do not have variable support for a driven member (i.e., a drive shaft) that is intermediate the distal ends. Typically, a support (such as a bearing) is provided at each opposite end. The shaft when under torque during cutting is apt to bend and can contact an interior of an outer protective shaft. This causes wear, damage, and excess noise, each of which further contribute to user fatigue.
It is especially desirable to include an intermediate support for a drive shaft of a pruning saw that prevents it from bending and contacting an interior of the outer protective shaft.
It is also desirable to vary the location of the intermediate support based on the degree of extensibility that is needed. For example, if an overall length of a motorized extensible pruning saw that included an extensible shaft drive was minimal, perhaps six feet in overall length, then an ideal position for the intermediate support of the shaft drive would be disposed at three feet, or about one-half of the overall length of the extensible portion.
If, however, the extensible pruning saw were extended to about ten feet of overall length then an ideal position for the intermediate support would be at five feet, again at about one-half of the effective length of the shaft drive. This is important because if the intermediate support remained at three feet then an unsupported remaining span of seven feet would exist. It is probable that under the increased torque that occurs during cutting (i.e., under load), the centrally disposed shaft drive would bend and possibly contact an interior of the outer shaft.
Even if the shaft failed to actually contact with an interior of the outer shaft, the arc where it bends introduces an eccentric by shifting mass to one side. This, in turn, causes vibration to occur. Vibration interferes with blood flow and can hasten the onset of fatigue.
The only two prior art known ways to prevent this from happening include increasing the inside diameter of the outer shaft to provide more room for the shaft drive to flex (i.e., bend) therein without contacting the interior of the outer shaft or to increase the rigidity of the shaft drive or both. Any of these approaches increase the overall weight of the tool (pruning saw). It is desirable that the pruning saw be as lightweight as possible to reduce operator fatigue.
No known prior art type of an extensible pruning saw includes a shaft drive (i.e., a motorized type of pruning saw) that is capable of providing an intermediate support that can vary its position relative to the amount that a variable extensible drive member has been extended or retracted.
Also, as mentioned hereinbefore, some limbs may be disposed at a greater height than any current type of extensible pruning saw can reach. There is a need to be able to provide a pruning saw with a greater maximum length of reach.
Also, when sawing limbs it is important to keep the teeth of the saw blade in contact with the limb and to do so while maintaining an ideal force that helps maximize the speed of cutting yet which does not needlessly add resistance to the blade.
A slight urging of the teeth of the blade into contact with the limb increases the rate of cutting that is occurring. Too much urging of the teeth into contact with the limb adds increased resistance during both the cutting stroke and also during the retraction stroke (i.e., when the blade is not cutting the limb) which decreases the rate of cutting that is occurring.
Also, when a limb overhead has been severed with a prior art type of pruning saws it falls as gravity dictates. Accordingly, it can at times descend like a sharpened spear toward the ground posing a severe risk of injury to the user as well as to any children, pets, or other bystanders.
Alternately, the limb can fall into a mass of branches and become stuck. Later, perhaps during a storm, it can fall unexpectedly again posing a severe risk of injury. There remains a need to control the severed limb, to direct it where desired, and to release it to fall only when the user is certain that it is safe underneath.
The need for control of the severed limb and the need to maintain cutting pressure on the limb during a cutting thereof are long-standing problems that have not heretobefore been solved.
Also, electric motors—whether powered by 120 VAC or battery, are generally expensive devices. If such a device must be included as a component part of a reciprocating pruning saw, then the cost of the product is substantially increased. It is desirable to provide a motorized type of a reciprocating pruning saw that does not include its own electric motor, but rather is adapted for use with a common type of electric motor that the vast majority of homeowners, tradesmen, and contractors already have and that is a portable electric drill.
Accordingly, it is also desirable to be able to provide a method for securing the reciprocating pruning saw to the electric drill that is effective, easy to use, and adapted for use with as many different models and types of electric drills as possible with a minimum number of different customized interfaces.
Accordingly, there exists today a need for a reciprocating pruning saw that helps to ameliorate the above-mentioned problems and difficulties as well as help to ameliorate those additional problems and difficulties as may be recited in the “OBJECTS AND SUMMARY OF THE INVENTION” or discussed elsewhere in the specification.
Clearly, such an apparatus would be a useful and desirable device.
2. Description of Prior Art
Saws are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. 6,820,339 to Albrightson, that issued on Nov. 23, 2004;
U.S. Pat. No. 6,651,348 to Steinmann, that issued on Nov. 25, 2003;
U.S. Pat. No. 6,264,211 to Granado, that issued on Jul. 24, 2001;
U.S. Pat. No. 5,755,293 to Bourke, that issued on May 26, 1998;
U.S. Pat. No. 5,595,250 to Bourke, that issued on Jan. 21, 1997;
U.S. Pat. No. 5,566,768 to Bourke, that issued on Oct. 22, 1996;
U.S. Pat. No. 5,607,265 to Lane, that issued on Mar. 4, 1997;
U.S. Pat. No. 5,185,934 to Tillman, that issued on Feb. 16, 1993;
U.S. Pat. No. 4,949,463 to Chen, that issued on Aug. 21, 1990;
U.S. Pat. No. 4,841,643 to Colela et al., that issued on Jun. 27, 1989;
U.S. Pat. No. 4,712,983 to Moynihan, that issued on Dec. 15, 1987;
U.S. Pat. No. 4,268,966 to Williams, that issued on May 26, 1981;
U.S. Pat. No. 3,755,896 to Tommerup, that issued on Sep. 4, 1973;
U.S. Pat. No. 2,881,519 to Gardner, that issued on Apr. 14, 1959;
U.S. Pat. No. 2,793,661 to Olson, that issued on May 28, 1957;
U.S. Pat. No. 2,713,271 to Dodegge, that issued on Jul. 19, 1955;
U.S. Pat. No. 2,631,619 to Folli, that issued on Mar. 17, 1953;
U.S. Pat. No. 2,621,685, to Butz, that issued on Dec. 16, 1952;
U.S. Pat. No. 2,211,741 to Elwell, that issued on Aug. 13, 1940; and
U.S. Pat. No. 1,481,055 to Fullbright, that issued on Jan. 15, 1924.
While the structural arrangements of the above described devices may, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.